Paper sizing



PIER SHG .liames Carl Schmidt, illollingswood, N. .lL, assignor to E. I. du Pont dc Nemours & Company, Wilmington, Del, a coration of lllielaware No Drawing. Application august as, 1935, Serial No. 38,329

This invention relates to the sizing of paper, more particularly to the sizing of calcium carbonate filled paper.

By the word size as employed herein is meant a water solution, dispersion or emulsion of a water resistant substance that is used to render paper fibers and filling pigments water resistant when dry; by sized is meant the condition of having been treated with a size; and by "sized paper is meant paper that is water resistant.

The standard procedure used in the paper industry for beater sizing paper by the addition to the pulp of a soap such as rosin size followed by the addition of an acidic precipitant such asalum, is not operable with calcium carbonate filled paper because the admixture of calcium carbonate with pulp slurry that has been so treated with a size and acidic size precipitant causes the liberation of carbon dioxide which forms a stable foam that results in' serious operating difiiculties in sheet formation on a Fourdrinier paper machine, and also because the size efiiciency of rosin size is practically destroyed by the alkalinity of calcium carbonate.

As a means for overcoming the above disclosed disadvantages it has been proposed to precipitate a protective barrier of paraihn on the calcium carbonate particles by adding alum to a mixture of paraflin emulsion and calcium carbonate slurry and then adding the treated slurry to pulp sized with rosin. Practical experience, however, has shown that the method just mentioned does not eliminate the difficulties incident to foaming.

'An object of this invention is to provide a practical process for the production of a hard sized paper filled with calcium carbonate. Another object is to provide a process for sizing calcium carbonate filed paper whereby acidicsize precipitants can be used without the formation of foam that impairs proper sheetformation on the paper machine. Still another object is to provide an improved process for the incorporation of size onto the fibers and onto the calcium carbonate in the production of a calcium carbonate filled paper. Further objects will appear hereinafter.

These objects are accomplished by a process, described more fully below, in which the acidity of the pulp is neutralized after precipitating the size onto the fibers with acidic precipitant.

The steps involved in my process are generally as follows: A water resistant sizing material in the form of an aqueous emulsion dispersion, or solution is incorporated into paper pulp and an acidic precipitant is added to set the water resistant substance onto the fibers. The acidity of the pulp is then neutralized by the addition of an alkali that does not liberate carbon dioxide on reaction with an acid. This non-acidic, sized paper pulp is then mixed with a calcium carbonate slurry that has been treated with a water resistant substance insensitive to the alkalinity of calcium carbonate. The stock is then formed into paper by regular paper making procedure. A well-formed and highly water resistant sheet of calcium carbonate filled paper is produced.

The preparation of a non-acidic, sized pulp by the process of this invention is carried out as follows: A size in the form of a water emulsion, 1

dispersion or solution is added to paper pulp in a beater or any other suitable mixing container, and the size is thoroughly mixed with pulp. An acidic precipitant, preferably alum, is next added in an amount sufiicient to lower the pH to about 4.8, which causes the size to be deposited in an insoluble form onto the fibers. The acidity of the pulp is then neutralized by the addition of an alkali. For this purpose I prefer to use a weak alkali such as ammonium hydroxide, but a strong alkali such as sodium hydroxide is also operable. However, the neutralizing alkali shouldnot be one that liberates'gas on acidification. The alkali is carefully added as a dilute solution so that highly alkaline localized areas are not formed. The pH'of the pulp after neutralization may be between 7.0 and 7.5. The amount of alkali added for neutralization is, however, controlled chiefiy by the degree of foaming experienced. The process is one of removing acid, which would otherwise liberate carbon dioxide, to the point where sufficient freedom from foam permits practicable operation.

Examples of materials that I have found particularly suitable in the present process for sizing the fibers are as follows: resins plasticized with China-wood oil or mineral oils such as par afiin oil, and resins modified with waxes such as paraffin, Asiatic or Japan wax. Examples of suitable resins are: cumarone resins, damar, ester gum, rosin and rosin modified phenol-formaldehyde resins. The oil or wax should preferably constitute 20-40% by weight of the resin and oil or wax composition. The process of sizing the fibers is also operable with soaps that form a water resistant precipitate with alum although I prefer to use the above type compositions because they have greater efliciency. Examples of suitable soaps are rosin size and sodium stearate.

The resin-oil or resin-wax compositions cited above are incorporated into the paper pulp as water emulsions. It is important that the water emulsion possess excellent stability as a rather dilute emulsion, and that the dispersed phase should be finely divided. Such an emulsion is best prepared by first forming an organic solution of the size and then emulsifying this solution in water by means of a suitable emulsifying agent followed by homogenization of the emulsion in a colloid mill.

The sizing of the calcium carbonate is carried out as an operation apart from the sizing of the pulp. In the manufacture of a hard sized paper filled with calcium carbonate, the calcium carbonate particles should be sized as well as the ,fibers. The size should be insensitive to the alkalinity of calcium carbonate, and the resin-China wood oil, resin-mineral oil and resin-wax compositions cited above have also been found eminently suitable as sizes for the calcium carbonate. An emulsion of wax, such as paraffin, Asiatic or Japan wax may be used.

The preferred procedure for sizing the calcium carbonate is to add the size emulsion to a water slurry of the calcium carbonate, which is kept agitated during the mixing operation so that the size is uniformly distributed. A precipitant, such as, for example, sulfuric acid, alum or calcium chloride is then added to insure thorough setting of the size. A suitable amount of the precipitant is 1.7% of sulfuric acid or 5% of paper makers alum or calcium chloride by weight based;

on the calcium carbonate. This sized calcium carbonate slurry is then held for use in the paper making operation. In the sizing of the calcium carbonate, it is again very important that the emulsion should be very stable and that its dispersed phase should be finely divided. 7

The sized calcium carbonate slurry is added to the neutral or slightly alkaline paper pulp at any convenient point in the paper making system prior to the sheet forming wire. For example, this may be done in the beater, in the machine chest, ortat the regulating box. Following this admixture the stock is formed into paper in accordance with regular paper making procedures. The stock operates well on the paper machine without difficulties from foaming which are encountered when the acidity of the sized paper pulp is not neutralized before admixture with calcium carbonate.

The amount of size depends upon the degree of water resistance required in the sheet. This may be varied anywhere from a slack sized to a hard sized condition by proper regulation of the amounts of size materials. A satisfactory range is from 2 to 6% by weight based on the carbonate for sizing the carbonate and from 0.5 to 3.0% based on the weight of the fiber for sizing the fiber.

The following examples are illustrative of methods for practicing my invention:

Example I A beater is furnished with 50 parts of bleached soda pulp, and 50 parts of bleached sulfite pulp ,(air dry weight), and the usual amount of water.

aioaaai to circulate in the beater for several minutes and then 100 parts of a 0.1% ammonium hydroxide solution is added. This renders the pulp neutral.

To a calcium carbonate slurry consisting of 65 parts of calcium carbonate and 585 parts of water is added 65 parts of a 3% cumar resin-Asiatic wax emulsion described below. This is followed by 65 parts of a 1.7% sulfuric acid solution and then 65 parts of a 5% solution of a heavy boiling corn starch. The calcium carbonate is thoroughly agitated during the entire mixing operation.

The sized calcium carbonate is now added to the pulp in the beater and the beating is continued for several minutes to obtain uniform mixing. The charge is then emptied from the heater and diluted with water to a suitable paper making consistency. The diluted stock is then formed into sheets, which are pressed and then dried at 100-110 C.

A 50-pound basis weight (25 x 38 x 500 ream) sheet containing 25% by weight of calcium carbonate, has a water resistance of 36 seconds by the standard dry indicator test.

The 3% cumar resin-China wood oil emulsion is prepared as follow: '70 parts of V- A; cumar resin, 30 parts of a heat bodied China-wood oil (viscosity of Y at 77 F. on Gardner-Holdt scale) and 10 parts of linseed oil acids are dissolved in 50 parts of solvent consisting of equal parts by weight of toluene and xylene. This solution, heated to 110 0., is added together with 40 parts by weight of a 5% ammonium hydroxide solution to 800 parts by weight of water at C. The water is-agitated with a high speed stirrer during this mixing operation. This emulsion is then homogenized by passing it twice through a colloid mill. The emulsion is then diluted to a 3% concentration by stirring in 2,333 parts of water at 70 to 80 C.

The 3% cumar resin-Asiatic wax emulsion is prepared as follows: 70 parts by weight of V cumar resin, 30 parts by weight of Asiatic wax, 10 parts by weight of linseed oil acids are dissolved, emulsified, homogenized, and diluted by the same procedure described above.

Example II The beater is furnished with 80 parts of soda pulp, 20 parts of bleached sulfite (air dry weight), and the usual amount of water. After the pulp is properly beaten, the furnish is dropped to a beater chest equipped with an agitator. To the pulp in the chest is added 50 parts of 3% rosin size and 50 parts of a 3% solution of paper makers alum, with thorough mixing after the addition of each. The pulp is allowed to stand for several minutes and then a 0.1% solution of sodium hydroxide is added in an amount sufiicient to bring the pH back to about 7.0. The pulp then passes through a Jordan machine, into a machine chest, and thence to the regulating box where it is diluted to the usual paper making consistency with water containing sized calcium carbonate in suspension. The diluted stock is then run off as paper on a Fourdrinier paper machine operating at a speed of 200 feet per minute.

The calcium carbonate is sized as follows: To parts of a.17.8% water slurry of calcium carbonate is added 35.6 parts of a 3% cumar resin- Asiatic wax emulsion described under Example I. This is followed by the addition of 17.8 parts of a 1.7% solution of sulfuric acid, and then 26.7 parts of a 4% solution of a heavy boiling corn 5 0 The calcium carbonate slurry is well the paper will contain 18% by weight of calcium.

carbonate. 7

A 43-pound basis weight sheet containing 18% by Weight of calcium carbonate has a water resistance of 25 seconds by the standard dry indicator test. The stock operates well on the. paper machine without encountering dificulties in sheet formation caused by foaming, and the size materials are held in the sheet during sheet formation with the result that a hard sized sheet of calcium carbonate filled paper is produced.

In the above two examples, starch is added to the calcium carbonate slurry to improve the finish and strength of the paper.

My improved process is advantageously practiced in connection with fillers consisting of alkaline compounds of alkaline earth metals and combinations of these with magnesium hydroxide or magnesium basic carbonate. More generally, the process is applicable to fillers which impart an alkaline reaction to water and which liberate carbon dioxide on reaction with sulfuric acid.

Various size compositions may be used in the present process. The size for the fiber may be any material which can be successfully deposited onto the paper fibers as paper pulp and which will impart water resistance to the fibers in the form of a dry sheet of paper. The size for the calcium carbonate maybe any material which can be successfully incorporated into a calcium carbonate slurry and which will render the calcium carbonate particles water resistant when dry.

The neutralization of the pulp after sizing may be carried out with other alkalis, such as trisodium phosphate or sodium silicate. The solution of alkali may be added to the sized pulp at any point in the paper making system prior to the addition of the sized calcium carbonate slurry.

It isnot'of particular importance that the sized calcium carbonate slurry should be added at any particular time or at any particular point to the neutral, sized paper pulp. The only limitation is that thorough mixing should be accomplished before the stock passes onto the paper machine.

vAlthough a Fourdrinier paper machine is cited in the examples of this invention other types of machines such as cylinder, Harper Fourdrinier, etc., are operative with this invention.

' Although in the preferred practice of this invention both the fiber and the calcium carbonate are treated with size prior to their admixture, the invention may also be practiced by sizing only the fiber before mixing with calcium carbonate. The operation then comprises (1) treatment of the pulp with a size insensitive to the alkalinity of calcium carbonate or other alkaline fillers and precipitation of the size onto the fibers with an acidic precipitant, (2) acidity of the pulp by the addition of an alkali such as ammonium or sodium hydroxide, (3) admixture of the pulp with a calcium carbonate slurry; and (4) conversion of the pulp slurry into paper by procedures previously described. For example, under Example I similar results may be obtained by using an unsized calcium carbonate slurry, although in this case the amount of size applied to the pulp should be increased about 50% with a corresponding increase in the amount neutralization of the' of 0.1% ammonium hydroxide for neutralization of the sized pulp. 'In the operation of this modified process it is necessary to treat the pulp with a size that is effective in the presence of alkaline fillers such as calcium carbonate.

In the preparation of the size emulsion, a large variety of substances are suitable substitutes for linseed oil acids, such as, for example, stearic acid, oleic acid, sulfonated oils, petroleum sulfonic acids,'etc. These substances may also be used in the form of the sodium or ammonium salt, and many other substances known to have emulsifying properties are operable.

I This invention is usefulin the manufacture of various paper products such as book and magazine papers, lithograph papers, writing papers, base for coated papers, etc, in which an alkaline pigment is used.

It will be apparent from the foregoing description that I have provided a practical process for the production of a hard sized sheet of calcium carbonate filled paper Without encountering operating difficulties from foam during sheet formation on the Fourdrinier wire. Another advantage of my process is that acidic precipitants may be used in the sizing of paper pulp in the production of calcium carbonate filled paper.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to ,the specific embodiments thereof except as defined in the appended claims.

I claim:

1. In a process for manufacturing sized paper having an alkaline filler, the steps comprising precipitating size on paper pulp with an acidic precipitant, then neutralizing the acidity of the sized pulp with dilute alkali which does not liberate carbon dioxide, and then mixing the pulp with a water slurry of the alkaline filler treated with size comprising plasticized resin insensitive to the alkalinity of the filler.

2. A process for manufacturing sized paper having an alkaline filler which comprises precipitating size on paper pulp with an acidic precipitant, then neutralizing the acidity of the sized pulp with dilute alkali which does not liberate carbon dioxide, and then mixing the pulp with a Water slurry of the alkaline filler treated with size comprising plasticized resin insensitive to the alkalinity of the filler, and making the treated pulp into paper.

3. Aprocess for manufacturing sized paper hav-- ing an alkaline filler which comprises mixing 'paper pulp with a water emulsion of size comprising plasticized resin, precipitating the plasticized resin on the fibers of the pulp by means of an acid precipitant, then neutralizing the acidity of the sized pulp with an alkali which does not liberate carbon dioxide, and then adding to the pulp a water slurry of the alkaline filler sized with plasticized resin precipitated thereon from an aqueous emulsion of a solution of the plasti- 'cized resin in volatile organic solvent.

4. The process set 'forth in claim 1 in which said filler is calcium carbonate.

5. The process set forth in claim 3 in which said plasticized resin of the paper size is a resin plasticized with oil.

6. The process set forth in claim 3 in which said plasticized resin of the paper size is a resin plasticized with China-wood oil.

7. The process set forth in claim 3 in which said piasticized resin of the paper size is a. resin plasticized with wax.

8. The process set forth in claim 3 in which said plasticized resin of the filler size is a resin plasticized with oil.

9. The process set forth in claim 3 in which said plasticized resin of the filler size is a resin plasticized with China-wood oil.

JAMES CARL SCHIWIDT. 

